Small-Scale Solar Central Receiver System Design and Analysis
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SMALL-SCALE SOLAR CENTRAL RECEIVER SYSTEM DESIGN AND ANALYSIS A Thesis presented to the Faculty at California Polytechnic State University San Luis Obispo In Partial Fulfillment of the Requirements for the Degree Master of Science in Mechanical Engineering By Daniel James Murray June 2012 © 2012 Daniel James Murray ALL RIGHTS RESERVED ii COMMITTEE MEMBERSHIP TITLE: Small-Scale Solar Central Receiver System Design and Analysis AUTHOR: Daniel James Murray DATE SUBMITTED: June 2012 COMMITTEE CHAIR: Andrew Kean, Associate Professor of Mechanical Engineering COMMITTEE MEMBER: Jesse Maddren, Professor of Mechanical Engineering COMMITTEE MEMBER: Craig Baltimore, Professor of Architectural Engineering iii Abstract Small-Scale Solar Central Receiver Design and Analysis Daniel James Murray This thesis develops an analytical model of a small-scale solar central receiver power plant located at the California Polytechnic State University in San Luis Obispo, California at 35.28° N, 120.66° W. The model is used to analyze typical energy output at any time during the year. The power plant is designed to produce an output of 100 kW electrical power, and is supplemented by the combustion of natural gas. Methodologies for determining the proper size and layout of heliostats, optimal tower height, receiver size, and turbine engine selection are developed. In this specific design, solar shares of up to 73.2% and an annual average of 44% are possible through the use of a gas-solar hybrid microturbine engine. Larger solar shares are not possible due to the limited size of land (about 0.5 acres used for this project) which limits the number of possible heliostat installations. iv Table of Contents List of Figures ......................................................................................................................................... vii List of Tables ............................................................................................................................................ x Chapter 1: Introduction and Background ...................................................................................................... 1 1.1 Scope ............................................................................................................................................. 1 1.2 Introduction ................................................................................................................................... 1 1.3 Objective ....................................................................................................................................... 2 1.4 Background ................................................................................................................................... 2 1.4.1 Heliostats .............................................................................................................................. 5 1.4.2 Receivers ............................................................................................................................... 6 1.4.3 Towers ................................................................................................................................ 10 1.4.4 Gas Microturbines ............................................................................................................... 11 Chapter 2: Solar Radiation .......................................................................................................................... 14 2.1 Measuring Solar Radiation ......................................................................................................... 15 2.2 Modeled Solar Radiation ............................................................................................................ 16 2.3 Solar Geometry ........................................................................................................................... 17 2.4 Tracking the Sun ......................................................................................................................... 20 Chapter 3: Microturbine Analysis ............................................................................................................... 23 3.1 Microturbine Solar Modifications............................................................................................... 23 3.1.1 Calculation of State Points .................................................................................................. 25 3.2 Pressure Drop .............................................................................................................................. 28 3.3 Thermal Losses ........................................................................................................................... 31 Chapter 4: Field Efficiency ......................................................................................................................... 33 4.1 Atmospheric Attenuation ............................................................................................................ 33 4.2 Shadowing and Blocking ............................................................................................................ 34 4.3 Spillage ....................................................................................................................................... 34 4.4 Reflectivity and Soiling .............................................................................................................. 34 4.5 Cosine Efficiency ........................................................................................................................ 35 4.6 Heliostat Tracking....................................................................................................................... 38 4.7 Total Field Efficiency ................................................................................................................. 38 Chapter 5: Design Parameters ..................................................................................................................... 39 5.1 Field Size .................................................................................................................................... 39 v 5.2 Tower Height .............................................................................................................................. 40 5.3 Heliostat Sizing ........................................................................................................................... 42 5.4 Receiver Sizing ........................................................................................................................... 43 5.4.1 Image Spread ...................................................................................................................... 43 5.4.2 Secondary Concentrator ...................................................................................................... 45 5.5 Field Layout ................................................................................................................................ 46 5.6 Tower Shadowing ....................................................................................................................... 50 Chapter 6: Performance .............................................................................................................................. 54 Chapter 7: Conclusions ............................................................................................................................... 57 References ................................................................................................................................................... 58 Appendix A: Thermodynamic Data .......................................................................................................... A-1 vi List of Figures Figure 1-1: The Solar One plant in Barstow, California [4]. ....................................................................... 3 Figure 1-2: The PS10 Solar Power Plant, an 11 MW system in Sevilla, Spain. There are 624 120 m2 heliostats pointed at a 115 m high tower [5]. ................................................................................................ 4 Figure 1-3: In this view of the PS10, the dust in the air makes the reflected beams visible [6]. ................. 4 Figure 1-4: A heliostat containing a set of mirrors each individually pointed towards the tower [7]........... 5 Figure 1-5: Practical Solar 1 1 m heliostat used for small-scale applications [9]. ..................................... 6 Figure 1-6: The external receiver of the Solar One facility in Barstow, CA [7]. ......................................... 7 Figure 1-7: A cavity type receiver with four apertures [10]. ....................................................................... 8 Figure 1-8: A porous volumetric receiver [11]. ........................................................................................... 8 Figure 1-9: A pressurized volumetric receiver [14]. .................................................................................... 9 Figure 1-10: The clustering of pressurized volumetric receivers [14]. ...................................................... 10 Figure 1-11: The two main tower designs: free-standing steel (left) and concrete (right) [15]. ................ 11 Figure 1-12: Typical gas microturbine system schematic [16]. ................................................................. 12 Figure 1-13: Pressure-volume (left) and temperature-entropy (right) diagrams